True. Which is why vacuum source matters, and why Pontiac used a TVS switch to change between sources based on engine temp.

Don't know much about Holley calibration, but 66 would be very lean primary jets in a Rochester with stock rods.

Get rid of the acceleration knock before adding vacuum advance. Lock out the secondaries and see if it goes away or gets worse. It should be slower, but if primary mix is good it shouldn't knock. If it's worse or same, check the accelerator pump. If it's better, be sure there is fuel in the secondary circuit.